Application of the 3-D Hydro-Mechanical Model GEOFRAC in enhanced geothermal systems

Abstract

GEOFRAC is a three-dimensional, geology-based, geometric-mechanical, hierarchical, stochastic model of natural rock fracture systems. The main characteristic of GEOFRAC is that it is based on statistical input representing fracture patterns in the field in form of the fracture intensity P₃₂ (fracture area per volume) and the best estimate fracture size E[A]. Recent developments in GEOFRAC allow the user to calculate the flow in a fractured medium. For this purpose the fractures are modeled as parallel plates and the flow rate can be calculated using the Poisseuille equation. This thesis explores the possibility of the application of GEOFRAC to model a geothermal reservoir. After modeling the fracture flow system of the reservoir, it is possible to obtain the production flow rate. A parametric study was conducted in order to check the sensitivity of the output of the model. An attempt to explain how aperture, width and rotation (orientation distribution) of the fractures influence the resulting flow rate in the production well is presented. GEOFRAC is a structured MATLAB code composed of more than 100 functions. A GUI was created in order to make GEOFRAC more accessible to the users. Future improvements are the keys for a powerful tool that will let GEOFRAC to be used to optimize the location of the injection and production wells in a geothermal system.